Single Orthorhombic Phase Research Articles

Characterization of Proton-Conducting Y(CrO4)1-X (PO4) x As a Cathode Material of Proton-Conducting Ceramic Fuel Cells

It has been reported that proton conducting oxide such as BaCeO3 and BaZrO3 have high proton conductivity at intermediate temperatures, IT, around 400-600°C. Therefore, proton-conducting ceramic fuel cells (PCFC) attract much attention as IT-operating fuel cell system (IT-FC). Nonetheless, the current PCFC performance lags far behind the SOFC performance even at the ITrange of 400-600°C. One of the reasons for the deteriorated performance of PCFC is the lack of suitable cathode materials. Generally, oxide ion-electron mixed conductors such as La0.6Sr0.4Co0.8Fe0.2O3- δ(LSCF) are used for the PCFC cathode, but these reveal large overpotential since forming the limited reaction zone due to the mismatch of ionic carriers with electrolyte. Accordingly, there is motivation to develop the proton-electron mixed conductors which can be used in cathode conditions of fuel cells. Previously, we found that Y(CrO4)1-x (PO4) x solid solution (YCP) have proton-electron mixed conductivity in wet air atmosphere. Hence, it is motivated to use YCP as additives of cathode materials of PCFC in order to extend the reaction zone. In this work, we examined the fuel cells using composite cathode of YCP and LSCF. BaCe0.7Zr0.1Y0.2O3- δ(BZCY) was used as proton conducting electrolyte. Bulk electrolyte cell were constructed with a BZCY disc which were prepared by solid state reactive sintering (SSRS) method. The electrolyte precursor powder was prepared by mixing proper amount of BaCO3, CeO2, ZrO2, and Y2O3 according to the desired stoichiometry with the addition of 2.0wt.% NiO as a sintering aid. This mixture was ball-milled for 48 h and uniaxially pressed under 20 MPa for 1 min and then cold-isostatic-pressed under 100 MPa for 1 min. Finally, the green pellets were calcined at 1400°C for 18 h so as to obtain bulk electrolyte disc (2 mmd, 9 mmf). YCP powders were synthesized by pyrolysis of the mixed Y-Cr-P hydroxide precursor at 700°C for 3h in O2. The hydroxide precursors were prepared by coprecipitation method with (NH3)H2PO4, Cr(NO3)3 and Y(NO3)3. YCP powders dispersed in a-Terpineol were mixed with LSCF paste (NexTek) in the volume ratio of YCP:LSCF = 1:1. YCP-LSCF mixed pastes were screen printed on the side of BZCY electrolyte as a cathode and Pt paste as anode was applied to the opposite faces so as to form Pt|BZCY|YCP5/LSCF cell. Au wire was attached along the side of BZCY disc as a reference electrode by using Au paste. To investigate cathode polarization characteristics, the complex impedance measurements were carried out with the three-electrode cell. The XRD pattern indicated that a single orthorhombic perovskite phase of BZCY was prepared by the SSRS method. The density of the sintered pellets was about 90%. The bulk electrolyte cell with the YCP5/LSCF cathode gives OCV over 1.0 V and maximum power density about 40 mW cm-2 at 600°C. The complex impedance measurements indicate that the cells reveal two impedance arcs according to cathodic polarization in Nyquist plots. The semicircle appearing in high frequency region (104-102 Hz), SH, can be assigned to the charge transfer reaction between the electrolyte and the cathode and one in low frequency region (102-10-1 Hz), SL, can be attributed to the dissociative oxygen adsorption reaction. SH of the cell with YCP-LSCF composite cathode was smaller than that of the cell with LSCF cathode. On the other hand, the SL of the composite cathode cells was larger than that of the LSCF cathode cells. These results indicate that the interfacial charge transfer reaction is promoted by adding proton-conducting YCP because of the extension of the electrode-electrolyte-air three phase boundary.

Oxygen Generation from 18oxygen-Doped Li2CuO2 Caused By Electrochemical Oxidation

INTORDUCTION Li-ion batteries with high energy density have been required for power sources of electric vehicles. In particularly, it is crucial that the positive electrodes exhibit a large specific capacity with high cell voltage. The practical candidates for the electrode are limited such as Li2MnO3-based solid solutions. Based on our previous investigations on LiNi0.5Mn0.5O2, we have focused on Li2CuO2 and Li2CuO2-Li2NiO2 solid solutions [1, 2, 3]. They have some unique advantages which are different from other popular positive electrodes. Firstly, copper has abundant resources and less toxicity compared to cobalt or nickel. Secondary, they expect to exhibit a high-capacity due to a large amount of Li like as Li2MnO3. Furthermore, they adopt mutually similar structure which has the square planner CuO4 with the copper atom in the center and the oxygen atoms at the corners. Thus, these structures lead to characteristics of electronic structure that Cu 3d and O2p orbitals overlap dominantly over a wide range of energy level. Hence, both copper and oxygen electrons in the Cu-containing oxides may participate in the electrochemical oxidizing and reducing reactions. Our ab-initio electronic calculation strongly suppports that electrons by electrochemical oxidation may be removed considerably from both copper and then oxygen atoms [1]. In addition, XRD patterns using synchrotron radiation showed the formation of CuO after the first charging [1, 2]. By combining our experimental and calculated results, oxygen could participate in charging process of Li2CuO2 and Li2CuO2-Li2NiO2solid solutions. The objective of this paper is to detect O2 release directly from 18O isotope-doped Li2CuO2 by use of GC-MS analysis, and then to discuss the role of the oxygen on the electrochemical mechanism of Li2CuO2 and Li2CuO2-Li2NiO2solid solutions. Experimental The samples for x = 0-0.4 in Li2Cu1-x Ni x O2 were prepared by a combination of co-precipitation and solid state reaction. The co-precipitates were obtained from Cu(CH3COO)2∙H2O and Ni(CH3COO)2∙4H2O by dropping 1 M LiOH solution. After heating dried co-precipitates at 873 K for 6 h in air, Cu and Ni oxides were obtained. They were mixed with chemical grade Li2O and sintered at 1073 K for 24 h under N2 flow. A sample for 18O isotope - doped was prepared by filling and sealing with 18O2 gas. Electrochemical testing was carried out by coin-type cells with Li/1M LiPF6 in EC:DMC(1:1)/samples at 298 K. The positive electrode was composed of the following materials; specimen: acetylene black: PTFE = 30:15:1.5 (wt.%). The rate of constant current was 1/20 C in the range of 2.0-4.3 V. The in-situelectrochemical testing cell was connected with GC-MS (Gas Chromatography Mass Spectrometry) analysis equipment and the measurement was performed with on-line to detect oxygen generation directly during charging process. RESULTS AND DISCUSSIONS All the obtained samples for 18O isotope-doped Li2CuO2 and x = 0-0.4 in Li2Cu1-x Ni x O2 showed an orthorhombic single phase and formed a Li2CuO2-Li2NiO2 solid solution. Fig.1(a) shows a charge curve of 18O-doped Li2CuO2 and GC-MS spectra collected at m/z = 35.90-36.40 is shown in Fig.1(b). The results of electrochemical testing were good agreement with those of our reported earlier [3]. A remarkable increasing of the detected intensity was observed from 4.1 to 4.3 V and then after the completion of the electrochemical testing the intensity decreased. Whereas, the intensity corresponding to the mass number of 36 was not detected for Li2CuO2 prepared by conventional oxygen gas. These results shows direct O2 gas generation clearly from Li2CuO2 by its electrochemical oxidation. On the other hands, the charge and discharge specific capacities increased with the amount of Ni contents. A reversible capacity of about 300 mAhg-1 for x = 0.3 in Li2Cu1-x Ni x O2 was obtained and the capacity was maintained after 10 cycles. Based on these results, we will discuss the role of the oxygen on the electrochemical mechanism of Li2CuO2 and Li2CuO2-Li2NiO2solid solutions. REFERENCES 1. Y. Arachi et al., J. Power Sources, 196, (2011) 6939. 2. Y. Arachi et al., Solid State Ionics, 225, (2012) 611. 3. Y. Arachi et al., ECS Trans, 50(2013)143. Figure 1

Plasma assisted synthesis and growth mechanism of rare V2O5 nanostructured thin films

In this communication, the authors have synthesized two rare nanostructures of V2O5 using facile plasma assisted sublimation process (PASP). V2O5 nanoflakes and nanoplates assembled in microspheres (NPMSs) was obtained on large area over nickel coated glass substrate using simple precursor of V2O5 pellets as source of oxide. The temperature of growth is varied along with time duration of deposition in order to obtain the different kinds of nanostructure as well as to understand the role of Ni-seed layer playing in controlling the overall morphology of nanostructures. The morphological, structural, and vibrational properties of V2O5 nanostructured thin films are systematically investigated as a function of time and deposition temperatures. Structural analysis carried out using the XRD shows the pure orthorhombic phase of V2O5 and revealed the dependence of crystallinity on the temperature and duration of growth. The Raman study of vanadium and oxygen atoms in nanostructured thin films (NTFs) is carried out by micro-Raman, which evidences the presence of single orthorhombic phase of V2O5 and accorded with XRD results. HRTEM analysis with SAED confirms that NFs and NPMSs are polycrystalline in nature. The stoichiometry ratio obtained from XPS analysis is ∼2.4, shows the compositional purity and stoichiometric nature of V2O5 NTFs. Based on the observed results a three steps growth mechanism is proposed.

Enhanced energy storage density and its variation tendency in CaZrxTi1−xO3 ceramics

The improved energy storage density and its variation tendency have been investigated for CaZrxTi1−xO3 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) solid solution ceramics. The dense ceramics with high bulk density above 97% could be obtained, and X-ray diffraction analysis confirms the orthorhombic single phase structure in all compositions. Substitution of Zr4+ obviously increases the sintering temperature, and the homogeneous fine grain structure is obtained. With increasing x, the dielectric constant εr decreases from 175 to 103, while the dielectric strength Eb increases from 435 kV/cm to 756 kV/cm. The highest energy storage density of 2.7 J/cm3 is achieved at x = 0.4, which is much higher than that of CaTiO3 end-member. The energy storage density significantly increases with decreasing the thickness due to the increased dielectric strength (For the samples with x = 0.5, the dielectric strength increases from 584 kV/cm to 756 kV/cm while the energy storage density increases from 1.6 J/cm3 to 2.6 J/cm3 when the thickness changes from 0.50 mm to 0.15 mm).

SnS thin films grown by sulfurization of evaporated Sn layers: Effect of sulfurization temperature and pressure

SnS thin films were grown by sulfurization of Sn layers evaporated by electron beam. The effect of sulfurization parameters, such as temperature and pressure, on the properties of tin sulfide layers has been investigated. Ar pressure used during the sulfurization has a strong impact on the development of a proper SnS/Mo back interface. However, the sulfurization temperature is the parameter that regulates the formation of an orthorhombic single phase SnS thin film with the optimum properties to be used as absorber for solar cell devices. Sulfurization temperature of 220°C for 240min led to the formation of single phase tin sulfide layers. Direct band gap energy about 1.2eV has been determined.

Electrodeposition and ab Initio Studies of Metastable Orthorhombic Bi2Se3: A Novel Semiconductor with Bandgap for Photovoltaic Applications

A metastable phase of Bi2Se3 with orthorhombic structure has been obtained by potentiostatic electrodeposition onto Si(100) substrate. The ideal stoichiometry and single orthorhombic phase could be obtained only within a restricted potential window, where mutual underpotential co-deposition is assumed to occur. Optical and electrical characterization indicates a bandgap of 1.25 eV, close to the maximum efficiency in the Shockley–Queisser limit, and n-type semiconducting behavior with moderate electrical resistivity. Theoretical calculations using density functional theory were used to support the structural and optical results. Due to the favorable set of properties with respect to isomorphic compounds such as Bi2S3, Sb2S3, and Sb2Se3, this material could lead to efficient and low-cost new thin film-based photovoltaic devices.

Aluminium bismuthate nanorods and the electrochemical performance for detection of tartaric acid

Aluminium bismuthate nanorods had been synthesized by a facile hydrothemral method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations showed that the lengh and diameter were 2–10 μm and 50–200 nm, respectively. X-ray diffraction (XRD) and high-resolution TEM (HRTEM) showed that the nanorods were composed of single crystalline orthorhombic Al4Bi2O9 phase. The aluminium bismuthate nanorods could be explained by the nucleation and crystalline growth process based on the products obtained from different hydrothermal conditions. Aluminium bismuthate nanorods modified glassy carbon electrode (GCE) was fabricated for the electrochemical detection of tartaric acid (TA) in neutral solution. A pair of semi-reversible redox peaks located at −0.08 V and −0.53 V, respectively were observed. The current intensity of the cyclic voltammogram (CV) peak increased linearly obviously with increasing the scan rate and TA concentration. The detection limit and linear range were 0.64 μM and 0.001–2 mM, respectively with the correlation coefficient of 0.995. The aluminium bismuthate nanorods modified GCE had good reproducibility and stability for the detection of TA.

Nano Perovskite SmFeO3 as an Electrode Material for Symmetrical Solid Oxide Fuel Cells

The nano SmFeO3-δ (SFO) perovskite oxide was synthesized by citric-acid method and assessed in regard to its possible use as an electrode material for symmetrical solid oxide fuel cells. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) confirmed that the SFO oxide prepared by this method had a single orthorhombic phase belonging to the Pnma (62) space group. Size of SFO nanoparticles, investigated by scanning electron microscope (SEM), was in the range of 200–400 nm. Analysis of electrical conductivity revealed that SFO was a p-type semiconductor. SFO had a good chemical compability with yttria stabilized zirconia (YSZ) electrolyte and showed no phase separation both in air and 5% H2/N2 atmospheres after calcination of 20 h at 850 °C. The SFO cathode and anode showed the lowest charge transfer resistances at 800 °C, 1.03 and 1.28 Ω cm2, respectively. Moreover, the SFO|YSZ|SFO symmetrical cell demonstrated performance with an open circuit potential of 0.96 V and peak power density of 6.85 mW cm-2 at 800 °C using humidified H2 as the fuel, respectively.

Structural and electrical properties of K-doped Sr1.85Ca0.15NaNb5O15 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics Sr1.85Ca0.15Na1−xKxNb5O15 (0.00≤x≤0.40) were prepared using the conventional solid state reaction method. The structural, dielectric and piezoelectric properties were systematically studied. All the ceramics are single orthorhombic tungsten bronze phase at room temperature, and the lattice constants increase with K+ content. The dielectric spectra of each composition had two dielectric anomalies. The Curie temperature Tc gradually decreases from 291°C to 266°C as x increase from 0.00 to 0.40, and the transition temperature Ts from orthorhombic phase to tetragonal phase increases from 39°C to 109°C. With increasing K+ contents, the piezoelectric coefficient d33 increases rapidly initially, reaches a maximum and then gradually decreases. The highest piezoelectric performance was obtained at x=0.10, with piezoelectric coefficient d33=114pC/N. Mechanisms that lead to the enhancement of d33 were discussed from the viewpoint of polarization and crystal structure.

Temperature and electric-field induced phase transitions, and full tensor properties of [011] C -poled domain-engineered tetragonal 0.63Pb(Mg1/3Nb2/3)-0.37PbTiO3 single crystals.

The phase-transition sequence of 0.67Pb(Mg1/3Nb2/3)-0.37PbTiO3 (PMN-0.37PT) single crystals driven by the electric (E) field and temperature is comprehensively studied. Based on the strain-E field loop, polarization-E field loop, and the evolution of domain configurations, the E field along the [011] C induced phase transitions have been confirmed to be as follows: tetragonal (T) → monoclinic (MC ) → single domain orthorhombic (O) phase. As the E field decreases, the induced O phase cannot be maintained and transformed to the MC phase, then to the coexistence state of MC and T phases. In addition, the complete sets of dielectric, piezoelectric, and elastic constants for the [011] C -poled domain-engineered PMN-0.37PT single crystal were measured at room temperature, which show high longitudinal dielectric, piezoelectric, and electromechanical properties ([Formula: see text], d33 = 1052 pC/N, and k33 = 0.766). Our results revealed that the MC phase plays an important role in the high electromechanical properties of this domain-engineered single crystal. The temperature dependence of the domain configuration revealed that the volume fraction of the MC phase decreases with temperature accompanied by the reduction of [Formula: see text], d31, and k31 due to the substantially smaller intrinsic properties of the T phase.

Compositional inhomogeneity and segregation in (K0.5Na0.5)NbO3 ceramics

In this report, the effects of the calcination temperature of (K0.5Na0.5)NbO3 (KNN) powder on the sintering and piezoelectric properties of KNN ceramics have been investigated. KNN powders are synthesized via the solid-state approach. Scanning electron microscopy and X-ray diffraction characterizations indicate that the incomplete reaction at 700°C and 750°C calcination results in the compositional inhomogeneity of the K-rich and Na-rich phases while the orthorhombic single phase is obtained after calcination at 900°C. During the sintering, the presence of the liquid K-rich phase due to the lower melting point has a significant impact on the densification, the abnormal grain growth and the deteriorated piezoelectric properties. From the standpoint of piezoelectric properties, the optimal calcination temperature obtained for KNN ceramics calcined at this temperature is determined to be 800°C, with piezoelectric constant d33=128.3pC/N, planar electromechanical coupling coefficient kp=32.2%, mechanical quality factor Qm=88, and dielectric loss tanδ=2.1%.

Structural and Electrical Properties of EOT HfO2 (

We report on changes in the structural, interfacial, and electrical characteristics of sub-1 nm equivalent oxide thickness (EOT) HfO2 grown on InAs by atomic layer deposition. When the HfO2 film was deposited on an InAs substrate at a temperature of 300 °C, the HfO2 was in an amorphous phase with an sharp interface, an EOT of 0.9 nm, and low preexisting interfacial defect states. During post deposition annealing (PDA) at 600 °C, the HfO2 was transformed from an amorphous to a single crystalline orthorhombic phase, which minimizes the interfacial lattice mismatch below 0.8%. Accordingly, the HfO2 dielectric after the PDA had a dielectric constant of ∼24 because of the permittivity of the well-ordered orthorhombic HfO2 structure. Moreover, border traps were reduced by half than the as-grown sample due to a reduction in bulk defects in HfO2 dielectric during the PDA. However, in terms of other electrical properties, the characteristics of the PDA-treated sample were degraded compared to the as-grown sample, with EOT values of 1.0 nm and larger interfacial defect states (Dit) above 1 × 10(14) cm(-2) eV(-1). X-ray photoelectron spectroscopy data indicated that the diffusion of In atoms from the InAs substrate into the HfO2 dielectric during the PDA at 600 °C resulted in the development of substantial midgap states.

Enhancing the Photocatalytic Activity of Sr4 Al14 O25 : Eu2+ , Dy3+ Persistent Phosphors by Codoping with Bi3+ Ions.

The photocatalytic activity of Bismuth-codoped Sr4 Al14 O25 : Eu2+ , Dy3+ persistent phosphors is studied by monitoring the degradation of the blue methylene dye UV light irradiation. Powder phosphors are obtained by a combustion synthesis method and a postannealing process in reductive atmosphere. The XRD patterns show a single orthorhombic phase Sr4 Al14 O25 : Eu2+ , Dy3+ , Bi3+ phosphors even at high Bismuth dopant concentrations of 12mol%, suggesting that Bi ions are well incorporated into the host lattice. SEM micrographs show irregular micrograins with sizes in the range of 0.5-20μm. The samples present an intense greenish-blue fluorescence and persistent emissions at 495nm, attributed to the 5d-4f allowed transitions of Eu2+ . The fluorescence decreases as Bi concentration increases; that suggest bismuth-induced traps formation that in turn quench the luminescence. The photocatalytic evaluation of the powders was studied under both 365nm UV and solar irradiations. Sample with 12mol% of Bi presented the best MB degradation activity; 310min of solar irradiation allow 100% MB degradation, whereas only 62.49% MB degradation is achieved under UV irradiation. Our results suggest that codoping the persistent phosphors with Bi3+ can be an alternative to enhance their photocatalytic activity.

Dosimetry characteristics of NaLi2PO4:Ce3+ OSLD phosphor

High Sensitivity NaLi2PO4:Ce3+ optically stimulated luminescence dosimetry (OSLD) phosphor material was prepared by a simple solid state diffusion method. The material was characterized by XRD to confirm its formation in a single phase. Comparison of the experimental data with that of the data available in the literature (JCPDF # 80-2110) shows formation of a single orthorhombic phase, with the space group Pmnb (62). Study on the particle size effect shows that particle size in the range 50–150μm is more suitable for the continuous wave-optically stimulated luminescence (CW-OSL) dosimetry. Dosimetric properties of the phosphor material (particle size 50–150μm) using CW-OSL technique for blue light stimulation (λ≈470nm) show that it is highly sensitive (~6 times more sensitive than the commercially available Al2O3:C phosphor) in the linear dose range. The phosphor has found to have all the other good dosimetric characteristics, such as, easy method of synthesis, tissue equivalence, i.e., low-Z material (Zeff. ~10.8), low fading (~ 25% in 20 days), wide range of dose response (3mGy–500Gy), easy optical bleaching for its reuse, excellent reusability, etc., which make it useful for OSL dosimetry of high-energy radiations. Another advantage of this OSLD phosphor is that its dosimetric TL glow peak does not fade much on taking OSL and thus it could also be used as TLD phosphor for re-estimating doses in case of any doubts.

Structural and optical properties of Nd3+ doped columbite SrNb2O6

Nd-doped SrNb2O6 particles have been prepared by a molten salt method using strontium nitrate, niobium oxide and NaCl–KCl salt mixture as a flux at a relatively low temperature as compared to solid-state reaction method. X-ray diffraction patterns of the pure SrNb2O6 samples exhibited a single orthorhombic phase. Photoluminescence (PL) properties of Nd-doped samples in near-infrared spectral region were studied in detail. A characteristic luminescence of Nd3+ at 1.06μm was observed for Nd-doped SrNb2O6. Concentration quenching phenomenon was detected depending on the Nd-doping concentrations at room temperature. This characteristic of the doped samples may be ascribed to the energy transfer between Nd3+ and niobate groups (NbO6).

Investigation of Boron-doping Effect on Photoluminescence Properties of CdNb2O6: Eu(3+) Phosphors.

Pure, Eu(3+)-doped and Eu(3+),B(3+) co-doped CdNb2O6 powders have been prepared by a molten salt synthesis method using Li2SO4/Na2SO4 salt mixture as a flux at a relatively low temperatures as compared to solid state reaction. X-ray diffraction patterns of pure CdNb2O6 samples indicated orthorhombic single phase. Photoluminescence investigations of CdNb2O6 samples showed a strong blue emission band centered at 460nm. For Eu-doped CdNb2O6 samples, the luminescence of Eu(3+) was observed with the host red emission varying with the Eu-doping concentrations. This PL characteristic of the doped samples may be attributed to the energy transfer between Eu(3+) and niobate groups (NbO6). Boron incorporation has remarkably increased the luminescence of Eu(3+)-doped CdNb2O6.

Effect of Na on the structural and electrical properties of lead-free sodium potassium niobate ceramics

K1-xNaxNbO3 (where x = 0.48, 0.53, 0.56 and 0.60) (KNN) perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that single orthorhombic phase was formed for KNN. Dielectric anomalies around 200°C and 370°C were identified as ferroelectric-ferroelectric and ferroelectric-paraelectric transition temperatures for KNN compound. The electrical behavior of KNN ceramics was studied by the help of impedance spectroscopy technique in the different temperature range. The impedance response in KNN ceramics could be resolved into a single contribution, associated with the bulk/grain. The conductivity studies confirm that the activation energies are strongly frequency dependent. A decreasing trend of Z′ with rise in temperature suggests the presence of negative temperature coefficient of resistance (NTCR) in the material in the low frequency region but tends to merge in the high frequency region at almost all temperatures.

Diffusion phase transition and impedance spectroscopy of Bi2O3/CuO co-doped BCZT lead-free ceramics

Perovskite type (Ba0.85Ca0.15−2xBi2x)(Zr0.1Ti0.9−xCux)O3 lead-free ceramics were prepared via a conventional solid-state reaction method. The phase structure, dielectric, ferroelectric properties and complex impedance were investigated in detail. XRD and dielectric measurements determined that single orthorhombic phase displayed in (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 at room temperature. With the introduction of Bi2O3/CuO, the phase structure exhibited the mixture of orthorhombic and tetragonal phases, and then turned to single tetragonal phase. In contrast to the sharp dielectric transition of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics, a broad dielectric peak coupled with a slight decrease in Curie temperature was observed in (Ba0.85Ca0.15−2xBi2x)(Zr0.1Ti0.9−xCux)O3 ceramics with increasing x. The observed diffuse phase transition behavior was further confirmed by a couple of measurements with polarization loops and polarization current density curves. The structural and the composition fluctuations induced by ions doping should be responsible for the diffuse phase transition behavior. Furthermore, physical mechanisms of the conduction and relaxation processes were revealed by using impedance spectroscopy analyses. It was concluded that the conduction and relaxation processes were thermally activated, which was closely linked with the singly and doubly ionized oxygen vacancies.

Synthesis, characterization and photoluminescence properties of Eu3+ doped columbite CdNb2O6

Pure and Eu3+-doped CdNb2O6 powders have been prepared by a molten salt synthesis method using Li2SO4/Na2SO4 salt mixture as a flux at relatively low temperatures as compared to solid state reaction. X-ray diffraction patterns of pure CdNb2O6 samples indicated orthorhombic single phase. Photoluminescence investigations of CdNb2O6 samples showed a strong blue emission band centered at 460nm. For Eu-doped CdNb2O6 samples, the luminescence of Eu3+ was observed with the host red emission varying with the Eu-doping concentrations. This PL characteristic of the doped samples may be attributed to the energy transfer between Eu3+ and niobate groups (NbO6).

X-ray Diffraction, Dielectric, and Raman Spectroscopy Studies of SrTiO3-Based Microwave Ceramics

xSrTiO3-(1 − x)Ca0.61Nd0.26TiO3 (SCNTx) and xSrTiO3-(1 − x)Na1/2La1/2TiO3 (SNLTx) ceramics were studied by x-ray diffraction and Raman spectroscopy in the composition range of 0.1 ≤ x ≤ 0.4. The x-ray patterns illustrated that the SCNTx (0.1 ≤ x ≤ 0.4) solid solutions had a single orthorhombic perovskite phase, while a single phase with pseudoorthorhombic structure was identified for the SNLTx (0.1 ≤ x ≤ 0.4) ceramics. In addition, the Lorentz fitting method was applied to separate the Raman spectra into several individual peaks. Meanwhile, the line shift and width of the main phonons are also discussed based on the Lorentz fitting method. Among these, some new peaks at about 470 cm−1/483 cm−1 and 442.31 cm−1/429.20 cm−1 appeared for the SCNTx and SNLTx samples with 0.3 ≤ x ≤ 0.4 due to A-site occupation by two or more types of cation with different electrovalence. Based on the resulting Q × f value and full-width at half-maximum of the A1g(O) stretch mode, it was found that propagation of microwave energy in the SCNTx samples showed stronger damping behavior; a smaller Q × f value was therefore expected with an increase in Sr content. Moreover, the τf value and tolerance factor (t) exhibited a proportional correlation because of increasing symmetry of the perovskite phase for the SNLTx (0.1 ≤ x ≤ 0.4) ceramics.